readBinFragments {R.utils} | R Documentation |
Reads binary data from disjoint sections of a connection or a file.
## Default S3 method: readBinFragments(con, what, idxs=1, size=NA, ..., verbose=FALSE)
con |
A connection or the pathname of an existing file. |
what |
A character string or an object specifying the the
data type (mode ()) to be read. |
idxs |
A vector of (non-duplicated) indices or a Nx2 matrix
of N from-to index intervals specifying the elements to be read. |
size |
The size of the data type to be read. If NA , the natural
size of the data type is used. |
... |
Additional arguments passed to readBin (). |
verbose |
A logical or a Verbose object. |
Returns a vector
of the requested mode
().
Henrik Bengtsson (http://www.braju.com/R/)
# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - # Create a data file # - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - data <- 1:255 size <- 2 pathname <- tempfile("exampleReadBinFragments") writeBin(con=pathname, data, size=size) # - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - # Read and write using index vectors # - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - # Read every 16:th byte in the file idxs <- seq(from=1, to=255, by=16) x <- readBinFragments(pathname, what="integer", size=size, signed=FALSE, idxs=idxs) stopifnot(identical(x, data[idxs])) print(x) # Update every 16:th byte in the file x0 <- x idxs <- seq(from=1, to=255, by=16) writeBinFragments(pathname, idxs=idxs, rev(x), size=size) x <- readBinFragments(pathname, what="integer", size=size, signed=FALSE, idxs=idxs) print(x) stopifnot(identical(rev(x0), x)) # Update every 16:th byte in the file idxs <- seq(from=1, to=255, by=16) writeBinFragments(pathname, idxs=idxs, rev(x), size=size) x <- readBinFragments(pathname, what="integer", size=size, signed=FALSE, idxs=idxs) print(x) stopifnot(identical(x0, x)) # Read the complete file x <- readBin(pathname, what="integer", size=size, signed=FALSE, n=length(data)) stopifnot(identical(x, data)) # - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - # Clean up # - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - file.remove(pathname)